xbee: receive messages from an interrupt - arduino

Question

I intend to read the data received by the xbee in an interrupt handler.
But as the handler can not use delays, I can not use readPacket (100).
I have the following code:
#include <XBee.h>
#include <avr/power.h>
#include <avr/sleep.h>
XBee xbee = XBee();
XBeeResponse response = XBeeResponse();
ZBRxResponse rx = ZBRxResponse();
int size;
uint8_t buffer[256];
void setup() {
Serial.begin(9600);
Serial1.begin(9600);
xbee.begin(Serial1);
attachInterrupt(0, wake_up_now, LOW );
}
void wake_up_now() {
xbee.readPacket();
if(xbee.getResponse().isAvailable()){
if (xbee.getResponse().getApiId() == ZB_RX_RESPONSE) {
xbee.getResponse().getZBRxResponse(rx);
size = rx.getDataLength();
for (int i = 0; i < size; i++)
buffer[i] = rx.getData(i);
}
}
}
void sleepNow() {
set_sleep_mode(SLEEP_MODE_IDLE);
sleep_enable();
power_adc_disable();
power_spi_disable();
power_timer0_disable();
power_timer1_disable();
power_timer2_disable();
power_twi_disable();
sleep_mode();
sleep_disable();
power_all_enable();
}
void loop() {
Serial.print("Awake");
Serial.println(size);
for (int i = 0; i < size; i++)
Serial.println(buffer[i]);
Serial.println("Entering Sleep mode");
delay(100);
sleepNow();
}
If you receive data the first time I can not read this data.
But later, when more data is received the data that was sent in the first message is read.
I really need to read the data in the handler, how can I solve this?

Answer 1

When I designed this ANSI C XBee Host library, I thought I could include frame processing as part of the serial interrupt handler on the Freescale HCS08 platform. I found that it just didn't work well, especially at a baud rate of 115,200.
The final design I went with was to keep a buffer of bytes from the serial port, and parse/dispatch frames in a "tick" function called in my main event loop. In one application, I was calling the "tick" function at least once every 50ms (IIRC).
As for forcing the XBee module to buffer serial data while you're sleeping, I think you'll have a hard time with that. You'd need to deassert RTS, but then wait to see if the XBee was still sending you a byte. My recollection is that I would still get multiple bytes (3 or 4?) after deasserting RTS. You'll also have to handle the condition of getting a partial packet while you're awake, and needing to decide whether you'll receive the whole frame then, or the next time you wake up.
You'd probably be better off using the XBee module's SPI interface, since the host controls when bytes are sent, and it might even be possible to have the XBee trigger a hardware interrupt on the host when it has bytes to send. You can also use high speeds (460kbps and up, I believe) to get the bytes quickly.